In general, microcantilever sensors are made of hard materials such as silicon, silicon nitride or silicon oxide. Accordingly, microcantilever sensors have a difficulty of response to weak stress or force and a limited applicability as sensitive sensors. In addition, it is very important to directly synthesize microcantilevers from soft and sensitive materials in order to use the same as certain biological/chemical sensors. One of effective materials in consideration of manufacturing possibility, stimuli-response and biocompatability is hydrogel.
Hydrogel microcantilevers were first synthesized by Toshiyuki Watanabe using two-proton polymerization reaction. In accordance with Watanabe's research, “Photoresponsive hydrogel microstructure fabricated by two-photon initiated polymerization”, found in Advanced Functional Materials of Wiley-VCH, in 2002, the attempt was encouraging, but there were problems in that synthesized microcantilevers had an extremely irregular thickness and process time was long.
Recently, flat hydrogel microcantilevers have been synthesized with three-dimensional stereolithography using focal lasers. These fine hydrogel microcantilevers can be synthesized to a length of 2 mm, a width of 2 mm and a thickness of 450 μm. Obviously, the length and width can be decreased as focus range of the laser becomes smaller. However, reduction in thickness of hydrogel microcantilevers remains unsolved due to limited permeation of lasers into hydrogels.